Beam tests of ionization chambers for the NuMI neutrino beam Page: 1 of 8
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St. Fermilab
WVFERMILAB-Conf-02/381-E September 2003
Beam Tests of Ionization Chambers
for the NuMI Neutrino Beam
Robert M. Zwaska, James Hall, Sacha E. Kopp, Huican Ping, Marek Proga, Albert R. Erwin, Christos Velissaris,
Deborah A. Harris, Donna Naples, Jeffrey McDonald, David Northacker, Milind Diwan, and Brett VirenCl
C
CAbstract-We have conducted tests at the Fermilab Booster of
ionization chambers to be used as monitors of the NuMI neutrino
beamline. The chambers were exposed to proton fluxes of up to
1012 particles/cm2/1.56ps. We studied space charge effects which
can reduce signal collection from the chambers at large charged
particle beam intensities.
Index Terms-Ionization chambers, ionizing radiation, multi-
plication, neutrinos, particle beam measurements, space charge.U I. INTRODUCTION
T HE Neutrinos at the Main Injector (NuMI) beamline at the
Fermi National Accelerator Laboratory [1] will generate
an intense v, beam from the decays of mesons produced in the
collisions of 120 GeV protons in a graphite target. The mesons
.-- are focused by magnetic "horns" into a 675 m evacuated
volume to allow decays to neutrinos. A downstream Alu-
_-_ minum/Steel absorber and bedrock absorb the remnant hadrons
and muons in the beam, leaving only neutrinos. The facility is
C expected deliver beam to neutrino experiments, beginning with
N the MINOS neutrino oscillation experiment, starting in early
2005.
The meson decays wr/K - pp, produce an energetic muon
for every neutrino, allowing monitoring and validation of the
neutrino beam focusing to be accomplished by monitoring of
the muon flux. As in several previous experiments, the muon
flux and remnant hadron flux at the end of the decay volume
will be measured by arrays of ionization chambers [2], [3], [4],
- [5].
The beam monitoring system will measure the intensity
and spatial distribution of the hadron beam at the end of
the decay tunnel, upstream of the absorber, and of the muon
beam after the absorber and at several stations in the bedrock.
The monitoring system will consist of 2 m x 2 m arrays of
Manuscript received December 2, 2002; This work was supported by the
U.S. Department of Energy, DE-AC02-76CH3000 and DE-FG03-93ER40757,
DE-FG02-05ER40896, and the Fondren Foundation.
R. M. Zwaska, J. Hall, S. E. Kopp, and M. Proga are with the Department
of Physics, University of Texas at Austin, Austin, TX 78712 USA (e-mail:
zwaska@mail.hep.utexas.edu; kopp@mail.hep.utexas.edu).
A. R. Erwin, H. Ping and C. Velissaris are with the Department of Physics,
University of Wisconsin at Madison, Madison, WI 53706 USA.
D. A. Harris is with the Fermi National Accelerator Laboratory, Batavia, IL
60510 USA.
D. Naples, J. McDonald, and D. Northacker are with the Department of
Physics, University of Pittsburgh, Pittsburgh, PA 15260 USA.
M. Diwan and B. Viren are with the Brookhaven National Laboratory, Upton,
NY 11973 USA.Hadron Near
Shielding Monit r Muon Detector
Monitors
Taret
H orns -
f 50m -- 675m
Dolomite Absorber
Fig. 1
PICTORIAL DIAGRAM OF THE NuMI BEAMLINE. THE 120 GEV PROTON
BEAM IS INCIDENT ON THE TARGET PRODUCING A HADRON BEAM. THE
POSITIVE HADRONS ARE FOCUSED BY THE HORNS, OF WHICH THE PIONS
TRAVEL INTO THE DECAY PIPE WHERE THEY DECAY INTO MUONS AND
MUON NEUTRINOS, MAKING THE NEUTRINO BEAM. THE HADRON MONITOR
AND MUON MONITORS MEASURE HADRON AND MUON FLUXES AT THEIR
LOCATIONS AND ARE CONSTRUCTED OF THE ION CHAMBERS DESCRIBED
HEREIN.
ionization chambers with 25 cm inter-chamber spacing, with
one chamber array in each of the above stations. The hadron and
muon fluxes are measures of any targeting or focusing failures.
The peak charged particle fluxes in one 9 ps accelerator burst
will be 2000, 25, 3, and 1.5 x 106/cm2 in the four monitoring
stations.
Each ionization chamber will measure the flux of charged
particles by using an applied electric field to collect the ion-
ization created in a helium gas volume. The charge measured
from each chamber will be proportional to the charged particle
flux at that location. By using an array of chambers the spatial
distribution of beam intensity can be inferred. While operated
without gas amplification the signal from the intense NuMI
beam in one 8 cm x 8 cm ionization chamber will be 33000,
1400, 170, and 83 pC at the four stations.
The individual ionization chambers within each array are
parallel plate chambers made up of two 4" square ceramic
plates with Ag-Pt electrodes. One plate has a single electrode
that applies HV bias. The second plate has two electrodes: a
central square sense pad measuring 3" x 3", surrounded by a
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al., Robert M. Zwaska et. Beam tests of ionization chambers for the NuMI neutrino beam, article, September 25, 2003; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc737543/m1/1/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.